1. Field of the Invention
The present invention relates to an inkjet printer system and an ink supply apparatus.
2. Discussion of the Background
An inkjet printer is an apparatus which forms images of information such as characters, graphics, patterns, and photographs on a print surface by ejecting fine particles of ink from a plurality of nozzles, which are formed in a print head, to deposit the ink on a print medium while moving the print head relative to the print medium. In the inkjet printer, since ink is consumed according to the ejection of the ink, a carriage of the print head or a printer body is provided with an ink tank (ink cartridge) having a volume based on the intended use. In case of a large-sized inkjet printer for printing commercial advertisements, banners, and the like, a large amount of ink is consumed in a relatively-short time. In such an industrial inkjet printer, therefore, a large volumetric ink tank is generally provided in the printer body, and the ink tank and the print head are connected through tubes or the like so as to supply ink from the ink tank to the print head according to the ejection of the ink.
As the inner pressure of the print head becomes higher than the normal atmospheric pressure, a problem that ink is pushed out of nozzles to drip onto a print medium, i.e. a dripping problem occurs. To solve this problem, in the inkjet printer, the ink supply device is adapted to control the inner pressure of the print head to be slightly lower than the normal atmospheric pressure, i.e. slight negative pressure. As one of conventional ink supply devices, there is known an ink supply device which includes an ink tank (main tank) disposed on a printer body and an ink replenisher (sub tank) having an ink chamber of a smaller volume disposed between the ink tank and a print head on a carriage, and which is of a “negative pressure producing type” in which the print head is made into a slight negative pressure by reducing the pressure of the ink chamber of the ink supply appratus (see, for example, JP-A-2004-284207 and JP-A-2006-62330).
The ink supply device of the aforementioned type is controlled such that a predetermined amount of ink is stored in the ink chamber of the ink replenisher according to the amount of ink ejected from the nozzles not to run out of the ink. As one example of the control, there is a method in which the level of the ink in the ink chamber is detected so that the control is conducted based on the detected level of the ink. Specifically, it is controlled to supply ink from the main tank to the ink chamber when it is detected that the ink level is lowered to a predetermined lower limit because of ejection of the ink from the nozzles. As a means of detecting the ink level in the ink chamber, a structure has been disclosed in JP-A-2001-141547 in which a float provided with a magnet is vertically movably placed to float on ink and a sensor (Hall element) for detecting magnetism from the magnet facing the sensor is disposed at a predetermined level (for example, the lower limit level). According to the aforementioned structure, the sensor can detect the magnetism from the magnet when faces the magnet. To improve the accuracy of magnetism detection, the vertical movement of the magnet is allowed but the magnet is restricted from freely rotating and swinging on the ink surface.
However, to precisely detect the ink level by the float to which the magnet is attached and which floats on the ink to move straight in the vertical direction according to the changes of the ink level as mentioned above, it is required to use a large float, for example, corresponding to the ink surface of the ink chamber in the ink replenisher. If such a large float is used, it is possible to detect precisely the ink level in the ink chamber of the ink replenisher, but there is a problem of limiting the volume for storing the ink in the ink chamber of the ink replenisher.